The aim of the proposed research is to investigate certain aspects of the molecular mechanism of gene expression in mammalian and other eukaryotic cells. We propose to continue our studies of the organization of nuclear ribonucleoprotein complexes containing hnRNA (nhRNP) sequences, and the role these structures play in the correct processing and splicing of mRNA sequences. Our previous results suggest a structure for hnRNP in which the large RNA molecule is folded on distinct protein complexes to give a repeating 30S RNP substructure. Most hnRNA and mRNA sequences are bound to these 30S subcomplexes but certain distinctive RNA regions are exposed or complexed with proteins other than the relatively simple set of polypeptides found in the 30S particles; for example self-complementary, or double-stranded RNA regions appear to be exposed while nuclear poly(A) is contained in a discrete 15S substructure within hn RNP. We have obtained electrophoretic and immunological evidence that the simple set of polypeptides that constitute the 30S RNP-core are relatively conserved amongst vertebrate organisms. We now intend to investigate in more detail the chemistry of these proteins, use dissociation-reconstitution systems to analyze the specificity of protein:protein and protein:RNA interactions, and employ our existing antibodies and newly-prepared monoclonal antibodies to examine the physiology of hnRNP complexes. Variations in the stoichiometry and metabolic properties of hnRNP core proteins suggest that they may be significant factors in the modulation of growth and differentiation of normal and transformed cells.